[foreign-memaccess] RFR: JDK-8243064: Add more support for mapped memory segments

[Maurizio Cimadamore]

This patch adds support for serial confinement - e.g. a handoff operation to transfer ownership from thread A to thread
B.

The implementation is based on some iterations we have done in the past. I've added a test, and I've also rewritten
some of the existing tests not to rely on waits, but to use latches instead, as observed by Paul.

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Commit messages:
 - * Add support for withOwnerThread operation

Changes: https://git.openjdk.java.net/panama-foreign/pull/117/files
 Webrev: https://webrevs.openjdk.java.net/panama-foreign/117/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JDK-JDK-8243064
  Stats: 142 lines in 5 files changed: 117 ins; 3 del; 22 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/117.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/117/head:pull/117

PR: https://git.openjdk.java.net/panama-foreign/pull/117